1. Field of the Invention
This invention relates to a communication apparatus, a method of communication, and a program executing a process for communication, which are preferably applicable to, for example, a wireless LAN (Local Area Network) system for data communication.
2. Description of Related Art
Conventionally, in wireless communication in which a predetermined transmission unit of packets are collectively transmitted, it is general that a structure of packet information of each transmission unit is determined in advance and the packet information is added to each packet to be transmitted.
On the other hand, in a rate variable transmission method for a general wireless communication system, it is known that transmission is carried out by a mechanism called fall back at a possible highest rate. When an error occurs, the transmission rate is decreased to a predetermined transmission rate for re-transmission.
In a rate variable control method for these wireless communication systems, there was proposed one in which header information includes rate information regarding a modulation process of a payload portion on the basis of a predetermined frame format. In the method, in a case where the header information can be decoded, a desired payload portion is decoded at a rate that is changed to the rate of the modulation process.
Here, in the conventional wireless communication system, a possible transmission rate is substantially determined in accordance with a bandwidth of a signal used in the wireless communication.
That is, in a certain wireless communication system, since a data rate for transmitting an application is substantially determined in accordance with its bandwidth. For example, an IEEE (The Institute of Electrical and Electronics Engineers) 802.11b-compliant wireless communication system has been designed to use a data rate of several megabits/sec and an IEEE 802.11a-compliant wireless communication system has been designed to use a data rate of tens megabits/sec.
Therefore, a fragment process and a frame structure, optimized for each wireless communication system, are specially prepared as a unique structure for each system.
FIG. 18 illustrates a MAC header structure defined in a small power data communication system/wireless 1394 system (ARIB STD-T72) (at page 102 of the standard book) as an existent data frame example.
The MAC header of this wireless communication system includes information such as a packet type, a transmission source station ID, a transmission destination station ID, a relay station ID, a B/E flag, a sequence number, and a data length (Length).
In such an existing wireless communication system, the MAC header information is formed in which information pieces of address information such as a destination and a transmission source, a sequence number, a data length, and presence and absence of a fragment are mixed.
FIG. 19 illustrates a MAC header and a frame body according to a frame format defined by the IEEE Draft P802.15.3/D16 standard (page 109) as an exemplary data frame structure of the existing technology according to Related Art.
In the figure, a MAC header includes a Frame Control (two Octets), a PN ID (two Octets), a Destination DEV ID (one Octet), a Source DEV ID (one Octet), a Fragmentation Control (three Octets), and a Stream Index (one Octet).
This case features that all address information pieces are represented by a DEV ID (device identifier). Further, contents of a predetermined fragment process are represented by a predetermined bit at a Fragmentation control field. In addition to the MAC header, a Frame Body (variable length) as a data payload and an FCS (4 Octets) for error detection constitutes a frame. Though it is not shown between the MAC header and the MAC frame in the figure, a header check sequence (HCS) may be further provided.
FIG. 20 illustrates a frame format defined by the IEEE Std 802.11, 1999 edition (at page 34) as an example of an existing data frame structure.
The MAC header includes a Frame Control (two Octets), a Duration ID (two Octets), an Address 1 (six Octets), an Address 2 (six Octets), an Address 3 (six Octets), a Sequence Control (two Octets), and an Address 4 (six Octets). In addition, a frame body (0-2312 Octets) as a data payload and FCS (four Octets) are also included therein.
Address fields of the Address 1 to the Address 4 in this configuration are occasionally assigned to a source address, a destination address, or the like, if necessary. Further, sequence number information and the like are described at the Sequence Control field.
FIG. 21 shows a fragment structure defined in the IEEE Std 802.11, 1999 edition (page 71) as an example of an existing fragmentation process.
In this fragment structure, a predetermined MSDU (MAC service data unit) is divided into four fragments, namely, Fragment 0 to Fragment 3. A MAC header and a CRC (Cyclic Redundancy Check) are added to each fragment. It is understood that, when the fragmentation process is executed, MAC header information is attached to each fragment.
FIG. 22 shows an example in which a plurality of MAC frame information pieces are formed in one PHY burst according to a related art technique. This shows that the sequences #1 to #3 are combined to form a single burst with once generated MAC header and FCS (CRC) attached thereto. That is, there exists each MAC header of the sequences #1 to #3 being multiplexed.
It is also understood that even if such a data frame format is adopted, a sequence number and fragment information of a data payload are necessary for each sequence, but the reception destination address information and the transmission source address information and the like are commonly used.
The Patent Document 1 cited below discloses an example of such a header structure.
[Patent Document 1]
Japanese Patent Application Publication No. Hei 10-247942
As described above, in the related art frame format, the MAC headers are generally multiplexed as they are. Thus, there is a problem that redundant fields such as address information exist at the MAC header more than the necessity.
Further, in a case where a predetermined transmission unit of packets are transmitted collectively, the same information such as address information is included as header information during transmission at each packet. Thus, there is a problem that such header information becomes redundant.